1. Field of the Invention
The present invention relates to an organic stripping composition and to an etching method using the same. More particularly, the invention relates to an organic stripping composition to prevent the generation of Si pitting and that effectively removes residues remaining after dry etching and ashing. The invention relates further to a method of etching an oxide using the composition.
2. Description of the Related Art
The design of semiconductor devices has recently made rapid progress as information media such as computers are becoming more popular widely used by the consuming public. In particular, this progress has required semiconductor devices to function at a high operating speed, and to have a large storage capacitance. Semiconductor devices having increased density, reliability, and response time currently are under development in an effort to satisfy such requirements.
The area of a chip increases by about 1.4 times in every three years, while the integration degree of a device increases by about 4 times to gradually reduce pitches between devices in a cell. When the pitch size between devices is reduced, it becomes increasingly difficult to manufacture devices that satisfy the two characteristics of insulation and refresh characteristics.
As the integration degree of semiconductor devices increases in order to increase productivity of chips within a limited area, multi-layered wirings have been developed and gradually minute patterns are formed. As the number of metal processes and via hole forming processes for the manufacture of the multi-layered wirings increases, various selective etching processes by means of a dry etching method are implemented. Photoresist patterns used as a mask during implementation of the dry etching method are removed after the dry etching by an ashing process. After completing the dry etching and the ashing process, various residues from dry etching gases, the photoresist, oxides, conductive thin films, etc. remain on the substrate surface. These residues mainly remain as a polymer and as impurities on a semiconductor device, which can increase the electrical resistance or induce an electric short. Accordingly, various stripping compositions are applied to efficiently remove these residues.
Japanese Patent Laid-Open Publication Nos. Sho 62-49355 and Sho 64-42653, disclose organic amine stripping solutions. These solutions include an alkane amine compound and an organic solvent. These stripping solutions typically are used at a relatively high temperature, however, and they include inflammable organic compounds that are liable to volatilize and are combustible. In addition, a metal film formed on the substrate may be corroded by an alkaline organic amine compound remaining on the substrate after the cleaning process when the substrate is cleaned using the organic amine stripping solution and then rinsed using water without applying an organic solvent such as an alcohol. Therefore, after cleaning the substrate, the substrate usually is rinsed using an organic solvent such as an alcohol.
In order to solve the above-described problem, Japanese Patent Laid-Open Publication Nos. Hei 7-201794 & Hei 8-20205 disclose an aqueous fluorine-based solution including a fluorine compound, an organic solvent, a corrosion inhibitor, etc. This aqueous solution is said to have an improved efficiency in removing residues and can be used at a low temperature.
However, when applying recent etching and ashing conditions, some residues still remain after stripping even when using the above-described organic amine stripping composition and the aqueous fluorine-based solution. The remaining residues increase the resistance of a semiconductor device and sometimes become a factor in forming a discontinuous conductive pattern of the device.
U.S. Pat. No. 6,323,169 issued to Abe et al., discloses a liquid-type resist stripping composition including an anti-oxidant, a chelating agent, an aqueous fluorine compound and optionally, an organic solvent. This patent alleges that residual resists remaining after etching can be effectively and clearly removed and various defects generated due to the residues can be minimized when applying this composition.
Recently, a fluorine-based organic stripping composition has been widely used. However, even though fluorine is effective for removing a polymer of oxide type, the main component of residues, stripping of other types of polymers is not effective. In addition, since this stripping composition is weakly basic, silicon (Si) might be etched as is the case with other compositions. When an organic stripping composition including fluorine is used, an oxide layer formed on the surface of an undesirably exposed Si by an etching process might be etched. Further, when Si (or Si substrate) is exposed to the stripping composition, Si might be excessively etched to generate a fatal Si pitting defect.
FIG. 1 is a cross-sectional view explaining one of the factors involved in generating an Si pitting defect, taken after implementing an etching process for forming a contact hole. A critical dimension obtained after cleaning inspection (ACI CD) was about 110±10 Å. A silicon nitride layer 14 is formed on a semiconductor substrate 10 that is divided into an active region and a field region by a field oxide layer 12 through an isolation process, and a gate 16 is formed on the active region of the substrate 10. At the side wall portion of the gate 16, a spacer 18 comprising silicon nitride is formed and a silicide layer 20 is formed of CoSi on a predetermined region of the substrate and the gate.
The silicide layer 20 is formed by a salicidation (self aligned silicide) process. Through the salicidation process, silicide regions where the silicide layer is formed can be selectively formed at desired regions. After depositing a metal such as Ti or Co and then heating the deposited metal, Ti-silicide or Co-silicide is formed when silicon atoms are present in the underlying layer. Through a patterning process of a subsequently formed insulation layer to form a contact hole, the silicide layer 20 is exposed. When a metal is deposited onto the exposed silicide layer 20, thus formed metal layer makes an advantageous contact with the silicon containing underlying layer through the medium of the silicide layer 20.
Besides the silicide layer 20, a wiring layer 24 comprising tungsten (W) and a first insulation layer 22 and a second insulation layer 26 (both comprising an oxide) are provided.
After completing an etching process for forming the contact hole, a first contact hole 31 for exposing the tungsten wiring 24, a second contact hole 32 for exposing a silicide layer on the gate and a third and fourth contact hole 33 and 34 for exposing the silicide layer 20 on the substrate are formed. The first, second and third contact holes 31, 32 and 33 are formed properly, however, the fourth contact hole 34 is not properly formed. Through the formation of the fourth contact hole 34, neighboring silicon substrate as well as the silicide layer is exposed as designated by region “A” in FIG. 1. During the formation of a contact hole by an etching process, a deviation of the position of the contact hole, that is, a misalignment, is inevitable, thereby generating the Si pitting problem.
One of the factors involved in generating the Si pitting phenomenon will be described in detail with reference to the above-described method of manufacturing a contact hole. First, a photoresist pattern used as a mask is removed after completing a dry etching process using gas plasma. In order to remove the photoresist pattern, two steps of an ashing process typically are employed: (i) one using oxygen; and (ii) the other using a stripping process using an aqueous alkaline solution. In detail, after anisotropically etching an insulation layer of an oxide by a dry etching, the photoresist pattern formed as the mask is removed through the ashing process. Through the ashing process, the photoresist of an organic polymer is evaporated under an oxygen plasma atmosphere as CO and CO2 through combustion. When a voltage of a high frequency is applied to an electrode in a chamber, an ashing gas plasma is produced. An activated ion of the plasma and material on the surface of the substrate are reacted with each other to evaporate the photoresist. After that, the substrate is treated using the stripping composition and then rinsed to remove residues to complete the etching process.
Most of the residual material remaining after the etching and ashing process is in the form of an oxide type polymer. In order to remove the oxide type polymer, an organic stripping composition is used. A fluorine-based organic stripping composition has recently been widely used as the stripping composition to improve the stripping property of the oxide type polymer as described above. However, since this composition is weakly basic, Si is etched by this composition with other chemical components. Accordingly, when the Si substrate is exposed to the stripping composition, Si is excessively etched to generate the fatal Si pitting defect.
FIGS. 2A and 2B are cross-sectional views that correspond to scanning electron microscope (SEM) pictures for comparing two Si substrates, wherein FIG. 2A is obtained when an Si pitting is not generated and FIG. 2B is obtained when an Si pitting is generated. After an oxide layer 22 is dry etched to form a contact hole, an ashing process and a cleaning process using an organic stripping composition are executed. When an amine-based stripping composition which does not contain fluorine is used as the stripping composition, a contact hole 30 including no Si pitting defect is formed as shown in FIG. 2A. However, when a basic stripping composition containing fluorine is used as the stripping composition, a contact hole 30 including an Si pitting defect is formed to generate a defect on a silicon substrate 10 as shown in FIG. 2B.
When the conventionally applied cleaning process using sulfuric acid that does not contain fluorine is used, the Si pitting is not generated. However, a defect is generated on an exposed tungsten (W) surface. For the manufacture of a device in which W is not exposed, the cleaning process using sulfuric acid usually can be applied. However, according to the trend of the manufacture of a semiconductor device having a high integration and a multi-layered structure, it is desirable to develop a unitary stripping composition that does not cause harm to almost all of the materials used, and that can be used in nearly all types of stripping processes.
The description herein of certain advantages and disadvantages of known compositions, and methods of their use, is not intended to limit the scope of the present invention. Indeed, the present invention may include some or all of the methods and chemical compositions described above without suffering from the same disadvantages.